Thermal treatment of capacitor electrode materials

ABSTRACT

Fabricating a capacitor includes performing an oxide formation operation on a sheet of material. The oxide formation operation forms an anode metal oxide on an anode metal. A thermal compression is performed on the sheet of material after the oxide formation operation is performed. The thermal compression applies thermal energy to the sheet of material while applying pressure to the sheet of material. After the thermal compression, the capacitor is assembled such that at least one electrode in the capacitor includes at least a portion of the sheet of material.

FIELD

The invention relates to electrochemical devices. In particular, theinvention relates to electrodes in capacitors.

BACKGROUND

In the current process for manufacturing aluminum electrolyticcapacitors, the anodes are typically punched or stamped from a sheet ofmaterial using a mechanical die. After the anodes are punched orstamped, the anodes are assembled into stacks with cathodes. Separatorsare positioned between cathodes and anodes that are adjacent to oneanother in the stack. The punching process can cause the edges of theanode to have burrs and other particles that can penetrate the separatorand cause a short in the capacitor or otherwise compromise the qualityand life of the capacitor.

Additionally, the physical stress of the punching or stamping processcan cause cracking of the anode. Tabs are often welded to the anodes toprovide electrical communication between the anodes and a terminal ofthe capacitor. The cracks formed by stamping or punching can propagatewhen welding the tabs to the anodes. Propagation of the cracks can causethe tabs to detach from the anode.

Further, the dies are made of steel and can contaminate the anode withiron particles. In addition to the iron penetrating the separator, theiron is also a source of corrosion that can lead to leakage andpremature capacitor failure.

For the above reasons, there is a need for improved capacitor anodes.

SUMMARY

Fabricating a capacitor includes performing an oxide formation operationon a sheet of material. The oxide formation operation forms an anodemetal oxide on an anode metal. A thermal compression is performed on thesheet of material after the oxide formation operation is performed. Thethermal compression applies thermal energy to the sheet of materialwhile applying pressure to the sheet of material. After the thermalcompression, the capacitor is assembled such that at least one electrodein the capacitor includes at least a portion of the sheet of material.

Fabricating an electrode for an electrochemical device can include lasercutting the anode from a sheet of material. The laser cutting can beperformed with any one, any two, any three, any four, any five, any six,or any seven parameters selected from the group consisting of a laserpulse duration greater than 0 s and less than a microsecond, a laserpulse frequency less than 2000 kHz, a pulsed laser spot overlap greaterthan 70%, a power density greater than 2×10⁵ W/cm², a scan rate greaterthan 100 mm/sec, a pass interval greater than 0.1 s, and a pass numbergreater that 10. The scan rate represents the rate at which the laserbeam is scanned across the sheet of material during laser cutting. Thepass number is the number of times that the laser beam is sequentiallyscanned along a pathway on the sheet of material in order to completelycut the anode from the sheet of material. The pass interval is theperiod of time that passes between each point along the pathway beingexposed to the laser beam. The electrochemical device can be a batteryor a capacitor. In some instances, the electrode is the anode of acapacitor such as an electrolytic capacitor. An example of anelectrolytic capacitor is an aluminum electrolytic capacitor.

Fabricating a capacitor can include obtaining a sheet of material havinga first phase of an anode metal oxide on an anode metal. The anode metaloxide is an oxide of the anode metal. A portion of the first phase ofthe anode metal is converted to a second phase of the anode metal oxide.At least a portion of the second phase of the anode metal oxide isremoved from the sheet of material. In some instances, the first phaseof the anode metal oxide is a dielectric while the second phase of theanode metal oxide is a conductor or a semiconductor.

The first phase of the anode metal oxide can be converted to the secondphase of the anode metal oxide as a result of the process used toextract a capacitor anode from the sheet of material. For instance, alaser can be used to cut the anode from the sheet of material and thelaser cutting can cause the conversion from the first phase to thesecond phase. In these instances, removing the portion of the secondphase of the anode metal oxide from the sheet of material can includeremoving the portion of the second phase from the anode.

The anode can be placed in a capacitor before removing the portion ofthe second phase of the anode metal oxide from the sheet of material.

In some instances, removing the portion of the second phase of the anodemetal oxide from the sheet of material is included in a cycle. The cyclecan also include an oxide restoration phase that forms the first phaseof the anode metal oxide on the anode or the sheet of material. In thecycle, the oxide restoration phase is performed after removing theportion of the second phase of the anode metal oxide from the sheet ofmaterial. In some instances, the cycle is performed at least twice.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A through FIG. 1G illustrate the construction of a capacitor. FIG.1A is a sideview of an anode that is suitable for use in the capacitor.

FIG. 1B is a cross-section of the anode shown in FIG. 1A taken along theline labeled B in FIG. 1A.

FIG. 1C is a sideview of a cathode that is suitable for use in thecapacitor.

FIG. 1D is a cross-section of the cathode shown in FIG. 1C taken alongthe line labeled D in FIG. 1C.

FIG. 1E is a cross section of an electrode assembly where anodes arealternated with cathodes. The anodes and cathodes can be constructedaccording to FIG. 1A through FIG. 1D.

FIG. 1F is a schematic diagram of a capacitor that includes theelectrode assembly of FIG. 1E positioned in a capacitor case.

FIG. 1G is a sideview of an interface between an anode and a cathodethat are adjacent to one another in the capacitor of FIG. 1F.

FIG. 2A through FIG. 2I illustrate a method of generating an anode foruse in a capacitor constructed according to FIG. 1A through FIG. 1G.FIG. 2A is a topview of a sheet of material from which the anode isconstructed. The sheet of material can be a sheet of an anode metal.

FIG. 2B is a portion of a cross section of the sheet of material showingan interface between the side of the sheet of material and theatmosphere in which the sheet of material is positioned.

FIG. 2C illustrates the sheet of material of FIG. 2B after the formationof preliminary channels in the sheet of material.

FIG. 2D illustrates the sheet of material of FIG. 2C after widening thepreliminary channels.

FIG. 2E illustrates the sheet of material of FIG. 2C after formation ofan anode metal oxide on the exposed surfaces of an anode metal.

FIG. 2F illustrates an example of a compression mechanism for performinga thermal compression operation on the sheet of material.

FIG. 2G illustrate an anode extracted from the sheet of material shownin FIG. 2F.

FIG. 2H is a top view of a portion of a sheet of material having a laserpathway with multiple different tracks.

FIG. 2I illustrates a capacitor that includes the anode of FIG. 2G.

FIG. 3A is a Scanning Electron Microscope image of an anode precursorwith re-solidified material present at the edge of the anode precursor.

FIG. 3B is a Scanning Electron Microscope image of an anode precursorwith re-deposited material present at the edge of the anode precursor.

FIG. 3C is a Scanning Electron Microscope of an anode precursor whereboth re-solidified material and re-deposited material are absent fromthe edge of the anode precursor.

FIG. 3D is a Scanning Electron Microscope of an anode precursor whereboth re-solidified material and re-deposited material are absent fromthe edge of the anode precursor.

FIG. 4A is a plot of deformation versus downs for multiple differentcapacitors that do not experience an oxide phase extraction.

FIG. 4B is another plot of deformation versus downs for multipledifferent capacitors that do not experience an oxide phase extraction.

FIG. 5A is a Scanning Electron Microscope image of an edge of an anodefrom a capacitor that does not experience an oxide phase extractionphase.

FIG. 5B is a Scanning Electron Microscope image of an edge of an anodefrom a capacitor that experiences an oxide phase extraction phase.

FIG. 6 is a plot of deformation versus downs for multiple differentcapacitors.

FIG. 7 is another plot of deformation versus downs for multipledifferent capacitors.

FIG. 8A is a picture of a sheet of material before a thermalcompression.

FIG. 8B shows the sheet of material of FIG. 8A after thermalcompression.

FIG. 9A is a plot of deformation versus downs for capacitors that wereeach generated without thermal compression.

FIG. 9B is a plot of deformation versus downs for capacitors that wereeach generated with a singled thermal compression.

FIG. 10 is a schematic diagram of a defibrillation system that includesan Implantable Cardioverter Defibrillator (ICD) that employs one or morecapacitors.

DESCRIPTION

The anodes for a capacitor can be cut from a sheet of material having alayer of an anode metal oxide on an anode metal. The layer of anodemetal oxide can be formed on the anode metal by alternating oxideformation operations with thermal treatments. The oxide formationoperation(s) form the anode metal oxide on the anode metal. The thermaltreatment(s) elevate the temperature of the sheet of material so as todrive water out of the anode metal oxide. The removal of this water hasbeen shown to improve leakage in capacitors. However, when thetemperature of the sheet of material is elevated to too high of atemperature and/or for too long of a time, the level of deformation canincrease. Deformation is a measure of how the amount of energy requiredto charge the capacitor changes over time.

The thermal treatments can each include one or more thermal compressionoperations. Thermal compression can include heating of the sheet ofmaterial while compressing at least a portion of the sheet of materialbetween multiple compression members. The direct contact between thecompression members and the sheet of material provides a highlyefficient transfer of thermal energy to the sheet of material. As aresult, the exposure of the sheet of material to elevated temperaturesduring the thermal treatment can be performed at lower temperaturesand/or for lower times. Accordingly, the use of thermal compression maybe able to remove water from the anode metal oxide while also reducingdeformation. As a result, the thermal compression can provide acceptablelevels of deformation and leakage.

Additionally, thermal compression can reduce warping of the sheet ofmaterial that occurs in response to processes used to fabricate of thesheet of material. The flattening of the sheet of material by thermalcompression can improve the processes used for extracting electrodesfrom the sheet of material. Capacitor anodes can be cut from the sheetof material using mechanical methods such as die cutting or usingnon-contact methods such as laser cutting. Mechanical cutting of awarped sheet of material can cause the sheet of material to move inresponse to the cutting operation. Laser cutting of a warped sheet ofmaterial causes the distance between the focal point and the sheet ofmaterial to change across the sheet of material. As a result, cutting ofwarped sheets of material provides inconsistent results. The flatteningof the sheet of material provided by thermal compression can reduce oreliminate these problems and increase the consistency of the cuttingresults.

The inventors have found that using lasers to cut anodes from the sheetof material can eliminate the mechanical damage, cracking, brokenparticles and the iron contamination associated with die cutting. As aresult, laser cutting can provide an increase in yield and efficiencythat translates into cost savings. The use of laser cutting also offersthe advantages of a process where changes in cutting dimensions fromroutine die wear are eliminated. Additionally, the size of the anodescan be changed simply by changing software instead of the delayassociated with mechanical die change outs and/or the obtaining of newdies.

The inventors have also found that laser cutting anodes from a sheet ofmaterial can be a source of DC leakage (“leakage”). For instance,portions of the sheet of material that melt during laser cutting cansolidify and stay on the resulting anode. Additionally or alternately,portions of the sheet can redeposit on the resulting anode. These excessmaterials can be a source of leakage and/or deformation in thecapacitor. Leakage is the amount of electrical current through thecapacitor when a voltage is applied across the capacitor. Deformation isa measure of how the amount of energy required to charge the capacitorchanges over time. Accordingly, increases in leakage and/or deformationare negative features for capacitor performance. The inventors havefound that leakage and/or deformation can be decreased by selectingvariables of the laser beam itself and/or by adjusting variables of thepath that the laser beam travels across the sheet of material.

The sheet of material from which the anodes are cut typically has alayer of an anode metal oxide on a layer of an anode metal. The anodemetal oxide is generally an oxide of the anode metal. The inventors havefound that laser cutting of the anodes from the sheet of material causesthe first phase of the anode metal oxide to be converted to a secondphase of the anode metal oxide.

In capacitors, such as electrolytic capacitors, the first phase operatesas the dielectric for the capacitor. However, the second phase is oftenmore electrically conductive than the first phase. For instance, thesecond phase can be a conductor or a semiconductor while the first phaseis a dielectric. This increase in conductivity is another source ofleakage in the capacitor. As an example, when the anode metal isaluminum, the oxide can be aluminum oxide. However, aluminum oxide canexist in one of several phases while in the same state. A first phase ofsolid aluminum oxide is called boehmite aluminum hydroxide (Al₂O₃) andacts as a dielectric. A second phase of solid aluminum oxide is calledalpha phase corundum oxide (α-Al₂O₃) and can act as a semiconductor. Theinventors have found that laser cutting can convert the boehmitealuminum hydroxide (Al₂O₃) to the alpha phase corundum oxide (α-Al₂O₃).This conversion has been found to be another source of capacitor leakageand deformation. Additionally, it has proven to be difficult to convertthe alpha phase corundum oxide (α-Al₂O₃) back to boehmite aluminumhydroxide (Al₂O₃).

The inventors have found that an oxide phase extraction can be used toremove at least a portion of the second phase of the anode metal oxidefrom the anode. For instance, the inventors have found that causing areaction between one or more components in an electrolyte in thecapacitor and the second phase of the anode metal oxide can move thesecond phase of the anode metal oxide off of the anode and into theelectrolyte. The inventors have found that removal of the second phaseof the anode metal oxide from the anodes reduces the leakage associatedwith the capacitor and accordingly reduces the deformation associatedwith the capacitor.

Capacitor deformation is an important measure for capacitor applicationswhere access to charging sources such as batteries is highly limited. Anexample of such an application is implantable medical devices such asImplantable Cardioverter Defibrillators (ICDs). ICDs include a batterythat charges the capacitors that are used to store the energy fordefibrillation shocks that are delivered to a patient. Reduced levels ofdeformation for the capacitors used in ICDs means that the amount ofenergy required to charge the capacitors is reduced. Accordingly, thereduced levels of deformation can increase the battery life and/orpermit the battery size to be reduced.

FIG. 1A through FIG. 1G illustrate the construction of a capacitor. FIG.1A is a sideview of an anode 10 that is suitable for use in thecapacitor. FIG. 1B is a cross-section of the anode 10 shown in FIG. 1Ataken along the line labeled B in FIG. 1A. The anode 10 includes,consists of, or consists essentially of a layer of anode metal oxide 12over a layer of an anode metal 14. Suitable anode metals 14 include, butare not limited to, aluminum, tantalum, magnesium, titanium, niobium,and zirconium. As illustrated in FIG. 1B, in some instances, the anodemetal oxide 12 surrounds the anode metal 14 in that the anode metaloxide 12 is positioned on both the edges and the faces of the anodemetal 14. Many anode metal oxides 12 can exist in more than one phasewithin the same material state (solid, liquid, gas, plasma). Forinstance, an anode metal oxide 12 such as aluminum oxide can be in aboehmite phase (Al₂O₃) that is a solid or in alpha phase corundum oxidephase (α-Al₂O₃) that is also a solid.

FIG. 1C is a sideview of a cathode 16 that is suitable for use in thecapacitor. FIG. 1D is a cross-section of the cathode 16 shown in FIG. 1Ctaken along the line labeled D in FIG. 1C. The cathode 16 includes alayer of cathode metal oxide 18 over a layer of a cathode metal 20.Suitable cathode metals 20 include, but are not limited to, aluminum,titanium, stainless steel. Although not illustrated, the cathode metalcan be layer of material on a substrate. For instance, the cathode metalcan be a titanium or titanium nitride coating on a substrate such as ametal and/or electrically conducting substrate. Examples of suitablesubstrates include, but are not limited to, aluminum, titanium, andstainless steel substrates. The cathode metal oxide 18 can be formed onthe cathode metal 20 by oxidizing the cathode metal 20 in air. Thecathode metal 20 can be the same as the anode metal 14 or different fromthe anode metal 14. In some instances, the cathode metal 20 and theanode metal 14 are both aluminum. As illustrated in FIG. 1D, in someinstances, the cathode metal oxide 18 surrounds the cathode metal 20.For instance, the cathode metal oxide 18 is positioned over the edgesand faces of the cathode metal 20.

The anodes 10 and cathodes 16 are generally arranged in an electrodeassembly 22 where one or more anodes 10 are alternated with one or morecathodes 16. For instance, FIG. 1E is a cross section of an electrodeassembly 22 where anodes 10 are alternated with cathodes 16. The anodes10 and cathodes 16 can be constructed according to FIG. 1A through FIG.1D. A separator 24 is positioned between anodes 10 and cathodes 16 thatare adjacent to one another in the electrode assembly 22. The electrodeassembly 22 typically includes the anodes 10 and cathodes 16 arranged ina stack or in a jelly roll configuration. Accordingly, the cross sectionof FIG. 1E can be a cross section of an electrode assembly 22 havingmultiple anodes 10 and multiple cathodes 16 arranged in a stack.Alternately, the cross section of FIG. 1E can be created by winding oneor more anodes 10 together with one or more cathodes 16 in a jelly rollconfiguration. However, as the anodes become more brittle due toincreased surface area, it may not be practical or possible to form ajelly-roll configuration. Suitable separators 24 include, but are notlimited to, kraft paper, fabric gauze, and woven for non-woven textilesmade of one or a composite of several classes of nonconductive fiberssuch as aramids, polyolefins, polyamides, polytetrafluoroethylenes,polypropylenes, and glasses.

The electrode assembly 22 is included in a capacitor. For instance, FIG.1F is a schematic diagram of a capacitor that includes the electrodeassembly 22 of FIG. 1E positioned in a capacitor case 26. Although notillustrated, the one or more anodes in the electrode assembly 22 are inelectrical communication with a first terminal 28 that can be accessedfrom outside of the capacitor case 26. The one or more cathodes 16 inthe electrical assembly are in electrical communication with a secondterminal 30 that can be accessed from outside of the capacitor case 26.In some instances, the one or more anodes include or are connected totabs (not shown) that provide electrical communication between the oneor more anodes and the first terminal 28 and the one or more cathodes 16include or are connected to tabs (not shown) that provide electricalcommunication between the one or more cathodes 16 and the secondterminal 30. The capacitor can include one or more electrical insulators(not shown) positioned as needed to prevent shorts-circuits within thecapacitor.

FIG. 1G is a sideview of an interface between an anode 10 and a cathode16 that are adjacent to one another in the capacitor of FIG. 1F. Theillustration in FIG. 1G is magnified so it shows features of the anode10 and cathode 16 that are not shown in FIG. 1A through FIG. 1E. Theface of the anode 10 includes channels 32 that extend into the anodemetal 14 so as to increase the surface area of the anode metal 14.Although the channels 32 are shown extending part way into the anodemetal, all or a portion of the channels 32 can extend through the anodemetal. Suitable channels 32 include, but are not limited to, pores,trenches, tunnels, recesses, and openings. In some instances, thechannels 32 are configured such that the anode has a number ofchannels/area greater than or equal to 30 million tunnels/cm².Increasing the number of channels has been shown to increase thebrittleness of the anodes and the sheet of material from which theanodes are extracted. Accordingly, increasing the surface area of theanode can result in a more brittle anode or sheet of material. The anodemetal oxide 12 is positioned on the surface of the anode metal 14 and ispositioned in the channels 32. The anode metal oxide 12 can fill thechannels 32 and/or anode oxide channels 34 can extend into the anodemetal oxide 12. However, it is generally not desirable for the anodemetal oxide 12 to fill the channels 32 because filling the channels 32can lead to reduced capacitance and electrical porosity.

The surface of the cathode 16 optionally includes cathode channels 36that extend into the anode metal 14 so as to increase the surface areaof the anode metal 14. Suitable cathode channels 36 include, but are notlimited to, pores, trenches, tunnels, recesses, and openings. Thecathode metal oxide 18 can be positioned on the surface of the cathodemetal 20. When the cathode metal 20 includes cathode channels 36, thecathode metal oxide 18 can be positioned in the cathode channels 36. Thecathode metal oxide 18 can fill the cathode channels 36 and/or cathodeoxide channels 38 can extend into the cathode metal oxide 18.

An electrolyte 40 is in contact with the separator 24, the anode 10 andthe cathode 16. The electrolyte 40 can be positioned in the cathodeoxide channels 38. When the cathode metal 20 includes cathode oxidechannels 38, the electrolyte 40 can be positioned in the cathode oxidechannels 38. The electrolyte 40 can be a liquid, solid, gel or othermedium and can be absorbed in the separator 24. The electrolyte 40 caninclude one or more salts dissolved in one or more solvents. Forinstance, the electrolyte 40 can be a mixture of a weak acid and a saltof a weak acid, preferably a salt of the weak acid employed, in apolyhydroxy alcohol solvent. The electrolytic or ion-producing componentof the electrolyte 40 is the salt that is dissolved in the solvent.

A capacitor constructed according to FIG. 1A through FIG. 1G can be anelectrolytic capacitor such as an aluminum electrolytic capacitor, atantalum electrolytic capacitor or a niobium electrolytic capacitor. Anelectrolytic capacitor is generally a polarized capacitor where theanode metal oxide 12 serves as the dielectric and the electrolyte 40effectively operates as the cathode 16.

FIG. 2A through FIG. 2I illustrate a method of generating an anode foruse in a capacitor constructed according to FIG. 1A through FIG. 1G. Asheet of material 48 can be acquired either by fabrication or purchasefrom a supplier. As will be evident below, one or more anodes areconstructed from the sheet of material 48. FIG. 2A is a topview of thesheet and shows a face of the sheet positioned between edges. FIG. 2B isa portion of a cross section of the sheet showing an interface betweenthe face of the sheet of material 48 and the atmosphere 50 in which thesheet is positioned. The sheet of material 48 can include, consist of,or consist essentially of the anode metal 14.

A surface area enhancement phase can be performed so as to increase thesurface area of the sheet of material 48. For instance, preliminarychannels 52 can be formed in the sheet of material 48 so as to providethe sheet of material 48 with the cross section of FIG. 2C. Suitablemethods of forming the preliminary channels 52 include, but are notlimited to, laser removal and/or drilling, etching such as chemicaletching and electrochemical etching. In one example, the etching iselectrochemical etching or electrochemical drilling. In electrochemicaletching and/or electrochemical drilling, the sheet of material 48 is atleast partially immersed in a bath that includes, consists of, orconsists essentially of an electrochemical drilling (ECD) solutioninitially having a pH of less than 5 while passing an electrical currentthrough the sheet of material 48. Additional examples of suitablemethods for forming the preliminary channels 52 and/or additionaldetails of suitable methods of electrochemical etching and/orelectrochemical drilling can be found in U.S. patent application Ser.No. 11/972,792, filed on Jan. 11, 2008, granted U.S. Pat. No. 8,535,527,and entitled “Electrochemical Drilling System and Process for ImprovingElectrical Porosity of Etched Anode Foil;” U.S. patent application Ser.No. 10/289,580, filed on Nov. 6, 2002, granted U.S. Pat. No. 6,858,126,and entitled “High Capacitance Anode and System and Method for MakingSame;” and U.S. patent application Ser. No. 10/199,846, filed on Jul.18, 2002, granted U.S. Pat. No. 6,802,954, and entitled “Creation ofPorous Anode Foil by Means of an Electrochemical Drilling Process;” eachof which is incorporated herein in its entirety.

In some instances, the surface area enhancement phase also includeswidening of the preliminary channels 52. Widening of the preliminarychannels can reduce or stop the anode metal oxide 12 from filling thechannels 32. For instance, the distance across the preliminary channels52 on the sheet of FIG. 2C can be increased to provide a sheet ofmaterial 48 having the channels 32 shown in the cross section of FIG.2D. In some instances, the preliminary channels 52 are formed andwidened so as to remove more than 52% or 60% of the sheet of material 48from the sheet of material 48 and/or to create more than 30 millionchannels/cm² of the sheet of material 48.

Suitable methods for widening the preliminary channels 52 include, butare not limited to, chemical and electrochemical processes. In oneexample of the widening process, widening of the preliminary channels 52includes immersing at least a portion of the sheet of material 48 in anelectrolyte solution that includes, consists of, or consists essentiallyof a chloride or nitrate. Additional examples of suitable methods forwidening of the preliminary channels 52 and/or additional details aboutthe above methods of widening preliminary channels 52 can be found inU.S. patent application Ser. No. 05/227,951, filed on Feb. 22, 1972,granted U.S. Pat. No. 3,779,877, and entitled “Electrolytic Etching ofAluminum Foil;” U.S. patent application Ser. No. 06/631,667, filed onJul. 16, 1984, granted U.S. Pat. No. 4,525,249, and entitled “Two StepElectro Chemical and Chemical Etch Process for High Volt Aluminum AnodeFoil;” U.S. patent application Ser. No. 11/972,792, filed on Jan. 11,2008, granted U.S. Pat. No. 8,535,527, and entitled “ElectrochemicalDrilling System and Process for Improving Electrical Porosity of EtchedAnode Foil;” U.S. patent application Ser. No. 10/289,580, filed on Nov.6, 2002, granted U.S. Pat. No. 6,858,126, and entitled “High CapacitanceAnode and System and Method for Making Same;” and U.S. patentapplication Ser. No. 10/199,846, filed on Jul. 18, 2002, granted U.S.Pat. No. 6,802,954, and entitled “Creation of Porous Anode Foil by Meansof an Electrochemical Drilling Process;” each of which is incorporatedherein in its entirety.

The anode metal oxide 12 is formed on the anode metal 14 that is exposedin the sheet of material 48. For instance, the anode metal oxide 12 canbe formed on the anode metal 14 that is exposed in FIG. 2D so as toprovide a sheet of material 48 according to FIG. 2E. The anode metaloxide 12 extends into the channels 32 so as to provide anode oxidechannels 34. Forming the anode metal oxide 12 on the exposed anode metal14 can include converting a portion of the existing anode metal 14 tothe anode metal oxide 12 or adding a layer of the anode metal 14 overthe previously existing anode metal 14. Converting a portion of theexisting anode metal 14 to the anode metal oxide 12 can include reactingthe anode metal 14 with a component such as oxygen. The anode metaloxide 12 is formed so the anode metal oxide 12 is in a first phase ofthe anode metal oxide 12. As an example, when the anode metal 14 isaluminum, the boehmite phase (Al₂O₃) of aluminum oxide is formed as theanode metal oxide 12. The first phase of the anode metal oxide 12 isdesirable for the final capacitor. For instance, the first phase of theanode metal oxide 12 generally serves as the dielectric for thecapacitor.

An example of a suitable method of forming the anode metal oxide 12 onthe anode metal 14 includes an optional hydration layer formationoperation, one or more oxide formation operations, and one or morethermal treatments.

The hydration layer formation operation forms a hydration layer indirect contact with the anode metal 14. The hydration layer can include,consist of, or consist essentially of the anode metal 14, hydrogen, andwater. For instance, the hydration layer can include, consist of, orconsist essentially of a hydrate of the anode metal 14. When the anodemetal 14 is aluminum, the hydration layer can include, consist of, orconsist essentially of aluminum hydrate.

In some instances, the hydration layer is formed on the anode metal 14by placing the sheet of material 48 in a bath liquid that includes,consists of, or consists essentially of water. In one example, the bathliquid is de-ionized water. The bath liquid may be held at a temperaturebetween 60° C. and 100° C. In some instances, the bath liquid ismaintained at about 95° C. The sheet of material 48 can remain in thebath liquid for a formation time. The formation time can be greater than1 minute and/or less than 20 minutes. The hydration can help form abetter quality oxide during the one or more oxide formation operations.

An example of a suitable oxide formation operation includes, but is notlimited to, mechanisms that convert existing anode metal 14 to anodemetal oxide 12 such as anodic oxidation. In anodic oxidation, the sheetof material 48 is placed in an electrolytic bath while a positivevoltage is applied to the sheet of material 48. The thickness of thelayer of anode metal oxide 12 can be increased by increasing the appliedvoltage. When the anode metal 14 is aluminum, anodic oxidation forms alayer of the boehmite phase of aluminum oxide (Al₂O₃) on a layer ofaluminum. In one example of anodic oxidation, the anode metal oxide 12is formed by placing the sheet of material in citric acid while apositive voltage of 400-550 volts is applied to the sheet of materialfor a period of time between 30 minutes to 150 minutes. Additionally oralternately, the electrical current that results from the appliedvoltage can be monitored and the sheet of material can be removed fromthe electrolytic solution in response to the electrical currentexceeding a treatment threshold.

The layer of oxide formed during the first oxide formation operationperformed on the sheet of material replaces and/or consumes thehydration layer formed during the hydration layer formation operation.As a result, the hydration layer is generally not present on the layerof material after the first oxide formation operation.

In some instances, the thermal treatments are each performed after anoxide formation operation. The thermal treatments elevate thetemperature of the sheet of material enough to drive out water from thelayer of anode metal oxide 12 formed during the previous oxide formationoperation(s). The removal of this water has been shown to decrease theleakage of capacitors. However, it is not desirable to remove all of thewater from the layer of anode metal oxide 12. Additionally, applyinghigh levels of thermal energy to the sheet of material can increase thelevel of deformation in a capacitor that includes an electrode made fromthe sheet of material. As a result, reducing the amount of thermalenergy applied to the sheet of material while removing this water maylead to both decreased leakage and decreased deformation.

A suitable thermal treatment includes one or more thermal compressionoperations. An example of a suitable thermal compression operation iscompressing the sheet of material between surfaces for a compressiontime with at least one of the surfaces having an elevated temperatureduring the compression.

FIG. 2F illustrates an example of a compression mechanism for performinga compression operation. The compression mechanism includes twocompression members. In FIG. 2F, a metal plate serves as each of thecompression members. Each of the compression members includes acompression surface that is in direct contact with the sheet of materialduring the compression operation. A contact portion of each compressionsurface is the portion of the surface that is in contact with the sheetof material during the compression operation. The location of thecontact portion on one of the compression members in diagram A of FIG.2F is illustrated by dashed lines.

As is evident from the arrow labeled C in FIG. 2F, the compressionmembers can be moved relative to one another. For instance, a first oneof the compression members can be immobilized while the secondcompression member is moved relative to the first compression member.Alternately, both of the compression members can be moved.

To prepare for the compression operation, the sheet of material isplaced between the compression members as shown in diagram A of FIG. 2F.The compression members are then moved relative to one another so thecontact portion of each compression surface is in direct physicalcontact with the sheet of material as shown in diagram B of FIG. 2F. Thecompression surfaces apply pressure to the sheet of material during thecompression operation. The compression operation continues for thecompression time that is desired for the compression operation. Afterthe compression time associated with the last compression operation isreached, the compression members can be moved apart and the sheet ofmaterial removed from between the compression members.

Although FIG. 2F shows the compression members as plates, thecompression members can be other components. For instance, one of thecompression members can be the side of an oven or the side of some otherstructure. Additionally or alternately, the compression members can bedifferent structures. For instance, one of the compression members canbe a plate as shown in FIG. 2F while another compression member is aside of an oven.

Although FIG. 2F shows the compression members as being independent ofone another, the compression members may be physically connected to oneanother. For instance, the compression members can be hinged or can bedifferent parts of a medium that is connected by a fold.

One or more of the compression members apply thermal energy to the sheetof material during a compression operation. For instance, the one ormore compression members can heat the sheet of material during acompression operation. As an example, the contact portion of one or moreof the compression surface can be at a compression temperature that isabove room temperature. One or more of the compression members caninclude a heating mechanism for bringing the contact portion of acompression surface to the desired compression temperature. Forinstance, a resistive heater can be mounted on a plate that serves as acompression member. Alternately, a plate that serves as a compressionmember can include one or more channels through which a heated fluid isflowed. In some instances, the heating mechanism for bringing one ormore of the compression surfaces to the desired compression temperaturecan be external to one or more of the compression members. For instance,the compression members can be located in an oven before and during thecompression treatment. As an example, the compression membersillustrated in FIG. 2F can be located in an oven before and during thecompression treatment. The oven can be maintained at the compressiontemperature in order to keep the temperature of the contact portion ofthe compression surfaces at the desired compression temperature.

Each of the compression operations in a thermal treatment is performedfor a compression time. The compression times associated with differentcompression operations can be the same or different. In some instances,the compression time is not long enough for the temperature of the sheetof material to reach the compression temperature. Accordingly, thetemperature of the sheet of material at the end of the compressionoperation (final operation temperature) can be different from thecompression temperature.

During a compression operation, a suitable pressure for applying to thesheet of material (compression pressure) is a pressure greater than 0.1ounce per square inch or 1 ounce per square inch and/or less than 0.1psi or 0.5 psi. During a compression operation, a suitable compressiontemperature for applying to the sheet of material is a temperaturegreater than 200° C., or 300° C., and/or less than 600° C., or 800° C.In some instances, the maximum temperature of the sheet of materialduring a compression operation is greater than 200° C., or 300° C.,and/or less than 600° C., or 800° C. Suitable compression times include,but are not limited to, compression times greater than 1 second, 5seconds and/or less than 10 seconds, 1 minute or ten minutes. In someinstances, the compression pressure and/or compression temperature areheld constant for the compression time during a compression operation.

In one example, a thermal treatment includes at least two compressionoperations performed at different pressure levels. A first one of thecompression operations can be a low pressure compression and a secondone of the compression operations can be a high pressure compression.The low pressure compression is performed at a lower compressionpressure than the high pressure compression. In some instances, the highpressure compression is performed immediately after the low pressurecompression without removing the sheet of material from between thecompression members and without other compression operations beingperformed between the low pressure compression and the high pressurecompression.

The low pressure compression can take advantage of the direct physicalcontact between the compression members and the sheet of material inorder to quickly elevate the temperature of the sheet of material towarda final operation temperature that is desired for the start of the highpressure compression. Suitable compression pressures for the lowpressure compression include, but are not limited to, pressures greaterthan 0.1 ounce per square inch or 1 ounce per square inch and/or lessthan 0.1 psi or 0.5 psi. Suitable compression temperatures for the lowpressure compression include, but are not limited to, temperaturesgreater than 200° C., or 300° C., and/or less than 600° C., or 800° C.Suitable final operation temperatures for the low pressure compressioninclude, but are not limited to, temperatures greater than temperaturesgreater than 200° C., or 300° C., and/or less than 600° C., or 800° C.Suitable compression times for the low pressure compression include, butare not limited to, times greater than 1 second, 5 seconds and/or lessthan 10 seconds, 1 minute or ten minutes. In some instances, the sheetof material is at or near room temperature before the low pressurecompression. In some instances, the compression pressure and/orcompression temperature are held constant or substantially constant forthe compression time during the low pressure compression.

The high pressure compression can be performed for a duration thatdrives out the water from the layer of anode metal oxide 12 and/or thatcauses cracks to form in the anode metal oxide 12. Suitable compressionpressures for the high pressure compression include, but are not limitedto, pressures greater than 0.5 psi and/or less than 1.0 psi or 2.0 psi.Suitable compression temperatures for the high pressure compressioninclude, but are not limited to, temperatures greater than 200° C., or300° C., and/or less than 600° C., or 800° C. Suitable compression timesfor the high pressure compression include, but are not limited to, timesgreater than 1 second, 2 seconds and/or less than 10 seconds, 1 minuteor ten minutes. In some instances, the compression temperatures for thehigh pressure compression are the same as the compression temperaturefor the low pressure compression. In some instances, the compressionpressure and/or compression temperature are held constant orsubstantially constant for the compression time during the low pressurecompression.

The increase in pressure between the low pressure compression and thehigh pressure compression can be done slowly. For instance, the increasein pressure can be at a rate greater than 0.0 psi/minute or 0.05 psi/minand/or less than 0.5 psi/min or 2 psi/min.

Various features of the method of forming the sheet of material asdisclosed in the context of FIG. 2A through FIG. 2F cause the sheet ofmaterial to warp. For instance, the channels 32 are generally not evenlydistributed across the sheet of material. Further, the morphology ofthese channels (i.e. straight channels, branched channels, etc.) is alsonot evenly distributed across the sheet of material. Additionally,forming the anode metal oxide 12 during the one or more oxide formationoperations generally causes the sheet of material to shrink. Forinstance, the one or more oxide formation operations performed whileforming the anode metal oxide 12 cause the volume of the sheet ofmaterial to decrease by as much as 15%. In some instances, the one ormore oxide formation operations performed while forming the anode metaloxide 12 cause the volume of the sheet of material to decrease by morethan 0.5%, or 1.5% and/or less than 4.5%, or 15%. The unevendistribution of the channels 32 combined with shrinkage of the sheet ofmaterial while forming the anode metal oxide 12 in these channels 32causes warping of the sheet of material. Other sources of warpinginclude, but are not limited to, the high voltages applied to the sheetof material during any anodic oxidation operations. Warped sheet ofmaterial tend to have multiple different peaks and valleys. In someinstances, the peaks and valleys have widths on the order of 0.1 to 0.5inches.

The thermal compression(s) in the thermal treatment can reduce warpingof the sheet of material. The elevated temperature combined with thecompression causes the sheet of material to adopt the shape of theinterface between the contact portions of each compression surface. Forinstance, in FIG. 2F, the contact portions are each flat or planar. As aresult, when the sheet of material adopts the shape of the interface,the sheet of material becomes flat or planar.

In some instances, one or more of the thermal treatments used whileforming the anode metal oxide excludes a compression operation. Forinstance, as few as one of the thermal treatments performed whileforming the anode metal oxide can include a compression operation whileall other thermal treatments each exclude a compression operation. Anexample of a thermal treatment that excludes compression can includeplacing a sheet of material in an oven at a thermal treatmenttemperature for a thermal treatment time but without compression of thesheet of material. Suitable thermal treatment temperatures include,temperatures greater than 100° C., or 300° C. and/or less than 600° C.,or 800° C. Suitable thermal treatment times include, times greater than10 second, 30 seconds, or 3 minutes and/or times less than 5 minutes or20 minutes.

When the method of forming the anode metal oxide 12 on the anode metal14 includes a hydration layer formation operation, the hydration layerformation operation can be performed before the one or more oxideformation operations and before the one or more thermal treatments. Whenthe method of forming the anode metal oxide 12 includes multiple oxideformation operations, the one or more thermal treatments can bealternated with the oxide formation operations. When the method offorming the anode metal oxide 12 on the anode metal 14 includes ahydration layer formation operation, the first oxide formation operationcan be performed between the hydration layer formation operation and thefirst thermal treatment. Additionally or alternately, the last oxideformation operation can be performed after the last thermal treatment orthe thermal treatment can be performed after the last oxide formationoperation. In one example of the method of forming the anode metal oxide12, the first oxide formation operation is performed between a hydrationlayer formation operation and the first thermal treatment; the one ormore thermal treatment are alternated with the one or more oxideformation operations; and the last oxide formation operation isperformed after the last thermal treatment. In another example of themethod of forming the anode metal oxide 12, the first oxide formationoperation is performed between a hydration layer formation operation andthe first thermal treatment; the one or more thermal treatments arealternated with the one or more oxide formation operations; and the lastthermal treatment operation is performed after the last oxide formation.

FIG. 2A through FIG. 2F illustrate a method of using fabrication toacquire a sheet of material 48 having a first phase of an anode metaloxide 12 on an anode metal 14. Alternately, any stage of the sheet ofmaterial 48 shown in FIG. 2A through FIG. 2F can be acquired by purchasefrom a supplier.

One or more anode precursors 56 are extracted from the sheet of material48. Accordingly, a portion of the sheet of material 48 serves as theanode precursor 56. Suitable methods of removing an anode precursor 56from the sheet of material 48 include, but are not limited to cuttingthe anode precursor 56 out of the sheet of material 48. A suitablemethod of cutting the anode precursor 56 out of the sheet of material 48include mechanical cutting method such as die cutting where the anodeprecursor is punched or stamped from a sheet of material using amechanical die. Another suitable method of cutting the anode precursor56 out of the sheet of material 48 includes no-contact cutting methodssuch as laser cutting of the anode precursor 56. FIG. 2G illustrates useof a laser 58 to cut anode precursors 56 out of a sheet of material 48constructed according to FIG. 2F.

The flat or planar shape of the sheet of material provided by thermalcompression can improve the cutting processes. Mechanical cutting of awarped sheet of material can cause the sheet of material to move inresponse to the cutting operation. Laser cutting of a warped sheet ofmaterial causes the distance between the focal point and the sheet ofmaterial to change across the sheet of material. As a result, cutting ofwarped sheets of material provides inconsistent results. The flatteningof the sheet of material provided by thermal compression can increasethe consistency of the cutting results.

As noted above, laser cutting may provide an increase in yield andefficiency when compared with mechanical cutting methods. Laser cuttingof the sheet of material can cause melted portions of the sheet ofmaterial to solidify and stay on the resulting anode precursor.Alternately, portions of the sheet can redeposit on the resulting anodeprecursor during the laser cutting process. These excess materials canbe reduced by using a pulsed laser beam. The short pulse durations thatare possible with pulsed lasers can provide very high peak powers formoderately energetic pulses. The increased peak power can providevaporization of the sheet of material during the laser cutting process.This vaporization can eject the material from any recess or trenchcreated in the sheet of material through the top of the sheet ofmaterial. Since the material is ejected from the sheet of material, thematerial is not available to re-solidify or re-deposit on the sheet ofmaterial.

In some instances, the duration of the pulse is greater than 0 s, or afemtosecond (10⁻¹⁵ s) and/or less than a microsecond (10⁻⁶ s). In oneexample, the duration of the pulse is greater than 100 femtoseconds andless than 900 femtoseconds. The time between pulses is inversely relatedto the pulse frequency. Suitable pulse frequencies can be greater than 0Hz, or 100 Hz, and/or less than 2000 kHz. In one example, the pulsefrequency is in a range of 200 kHz to 600 kHz. In some instances, theduration of the pulse is greater than 0 s, or a femtosecond (10⁻¹⁵ s)and/or less than a microsecond (10⁻⁶ s) and the pulse frequency isgreater than 0 Hz, or 100 Hz, or 100 kHz and/or less than 2000 kHz.

The power density of the laser beam at the sheet of material can be at alevel that a single pulse elevates the temperature of the sheet ofmaterial above the boiling point of the anode metal and vaporizes theanode metal. In some instances, power density of the laser beam is suchthat at least a portion of the sheet of material that is illuminated bythe laser reaches the boiling point of the anode metal and vaporizes ina period of time less than or equal to the duration of one pulse whenthe illuminated portion of the sheet of material is at temperature (23°C. or 25° C.) before the pulse. In an example where the anode metal isaluminum, the pulse duration is 820 femtoseconds, the pulse frequency is400,000 pulses per second, and the laser beam has a power density7.99×10¹¹ W/cm² at the surface of the sheet of material. Suitable powerdensities include, but are not limited to, power densities greater than0 W/cm², 1×10¹¹ W/cm², or 2×10⁵ W/cm² and/or less than 9×10¹¹ W/cm², or2×10⁵ W/cm¹². The combination of elevated power densities and reducedpulse durations reduces the amount of heat transferred to the sheet ofmaterial. However, adjusting these parameters may not be sufficient toaddress the increase in deformation that can result from using lasercutting of the anodes rather than stamped or punched cutting of theanodes.

The path of the laser beam across the face of the sheet of material canbe controlled by electronics and/or software. The electronics and/orsoftware can move the laser beam relative to the sheet of materialand/or the sheet of material relative to the laser beam. In FIG. 2G, thesolid lines and the dashed lines that show the outline of an anodeprecursor in the sheet of material represent the laser beam pathwayduring the process of cutting the anode precursor from the sheet ofmaterial. As a result, the laser is incident on the anode metal oxideduring at least a portion of the laser cutting.

The inventors have found that tuning the characteristics for the laserbeam path across the sheet of material can also reduce the leakage anddeformation to or even below the levels associated with stamping orpunching of anodes. For instance, the rate at which the beam is scannedacross the sheet of material can be tuned. Faster scan rates reduce theamount of energy that is absorbed by the anode precursor. In someinstances, the laser beam is scanned across the sheet of material at arate greater than 0 mm/sec, 100 mm/sec, or 600 mm/sec, and/or less than900 mm/sec, or 1100 mm/sec.

Reducing the spot size can also reduce the amount of thermal energytransferred to the sheet of material. Suitable spot sizes include, butare not limited to, spots having a diameter or major axis greater than10 microns, 30 microns and/or less than 50 microns, or 150 microns.Additionally or alternately, the spot size can be selected to producespot overlaps less than 100%. A spot is the area of the sheet ofmaterial illuminated by the laser beam during a pulse. Spot overlap isthe overlap of a spot with the spot provided by the previous pulse.Suitable spot overlaps include spot overlaps greater than 70%, or 90%and/or less than 100%. The spot size can be selected to provide theselevels of spot overlap when combined with the above scan rates and pulsefrequencies.

Increasing the beam scan rate can reduce the depth that the laser beamcuts into the sheet of material. As a result, multiple passes of thelaser beam along a pathway may be necessary in order to completely cutthe anode precursor out of the sheet of material. This result is evidentin the pathway labeled P FIG. 2G. The pathway includes dashed lines thatindicate where the laser beam has cut into the sheet of material withoutcutting through the sheet of material. The pathway also includes solidlines that indicate the portion of the anode precursor outline where thelaser beam has cut through the sheet of material. Additionally, thearrow labeled A indicates the direction of travel for the laser beamrelative to the anode precursor. At the start of the laser cutting, thelaser beam may be incident on the anode metal oxide. Once the laser beamhas cut through the anode metal oxide, the laser beam is incident on theanode metal.

The need for multiple passes of the laser beam in order to cut throughthe sheet of material means that each location along the beam pathway isnot exposed to the leaser beam energy for a pass interval. The passinterval can be the time between passes of the laser beam and/or can bethe period of time that passes between each point along the pathwaybeing exposed to the laser beam. Suitable pass intervals include, butare not limited to, pass intervals more than 0.1 seconds per pass and/orless than 3 seconds per pass. In some instances, the pass interval isselected such that more than 5, or 10 and/or less than 100 passes of thelaser beam around the entire outline of the anode precursor are requiredto completely extract an anode precursor from the sheet of material.

The laser pathway can include multiple different tracks. FIG. 2H is atop view of a portion of a sheet of material 48. A portion of a laserpathway on the sheet of material is labeled P. The laser pathwayincludes a first track 59 represented by dashed lines and a second track60 represented by solid lines. The first track 59 represents the trackthat the laser follows during a pass along the laser pathway. The secondtrack 60 represents the track that the laser follows during a differentpass along the laser pathway. The first track 59 has a width labeled wand the second track 60 has a width labeled W. When the first track 59and the second track 60 are followed by the same laser or by lasers withthe same spot size, the width of the first track 59 will be the same orabout the same as the width of the second track 60.

The second track 60 is offset from the first track 59 by a distancelabeled OS in FIG. 2H. The amount of offset can be selected such thatthe second track 60 partially overlaps the first track 59 as shown inFIG. 2H. The use of partially overlapping tracks while laser cutting theanode precursor widens the trench that the laser forms in the sheet ofmaterial to a width larger than the spot diameter. The cutting of awider trench can reduce the amount of thermal energy that is applied topreviously formed surfaces in the trench. The track overlap percentagecan be the overlap distance divided by the width of the overlappedtrack. Suitable track overlap percentages include, but are not limitedto, track overlap percentages greater than 25% or 30% and/or less than50% or 75%. The offset distance can be a function of spot size. Forinstance, when the spot size has a diameter of 40 microns, a suitableoffset distance can be any distance between 0 and 40 microns, such as 10to 30 microns.

In some instances, the different tracks extend around the perimeter ofthe anode and/or surround the perimeter of the anode. For instance, theentire length of the laser pathway shown in FIG. 2G can include twotracks that partially overlap, as shown in FIG. 2H. In other words, thelaser pathway of FIG. 2H can represent the laser pathway of any straightportion of the laser pathway shown FIG. 2G. Accordingly, the laser cantrace all, or substantially all, of the anode perimeter along one trackand later trace all, or substantially all, of the anode perimeter alonganother track that partially overlaps the prior track, as describedabove. Alternately, different tracks can partially overlap along one ormore portions of the anode perimeter but completely overlap along one ormore other portions of the anode perimeter.

Although the laser pathway in FIG. 2H is illustrated as having twotracks, the laser pathway can include a single track or more than twotracks. During the laser cutting process, a track can be followed onceor more than once. For instance, when a laser pathway includes twotracks as is shown in FIG. 2H, the laser can alternate between differenttracks on subsequent passes. As an example, the laser can follow thefirst track 59, the second track 60, the first track 59, the secondtrack 60, and so on until the trench extends through the sheet ofmaterial and the anode precursor is extracted from the sheet ofmaterial.

In some instances, the anode precursor is fabricated using one, two,three, four, five or six parameters selected from the group consistingof a laser pulse duration, pulse frequency, power density, scan rate,pass interval, and pass number. In these instances, the laser pulseduration is 400 femtoseconds, the laser pulse frequency is 400 kHz, thepower density is 7.99×10¹¹ W/cm², the scan rate is 720 mm/sec, the passinterval is 0.25 seconds, and the pass number is 60.

The inventors have also found that the use of a laser to extract the oneor more anode precursors 56 from the sheet of material 48 can convert atleast a portion of the first phase of the anode metal oxide 12 to asecond phase of the anode metal oxide 12. For instance, using a laser tocut a sheet of material 48 with aluminum as the anode metal 14 and theboehmite phase of aluminum oxide (Al₂O₃) as the anode metal oxide 12 canconvert the boehmite phase of aluminum oxide to the alpha-corundum oxide(α-Al₂O₃) phase of aluminum oxide. This conversion is believed to be aresult of the heat generated during the laser cutting process. As aresult, the conversion primarily occurs at and/or near the edge of theanode precursor 56. The second phase of the anode metal oxide 12 isoften undesirable. For instance, the second phase of the anode metaloxide 12 can be more electrically conductive than the first phase of theanode metal oxide 12. As an example, the alpha corundum oxide (α-Al₂O₃)phase of aluminum oxide has properties of a semiconductor. As a result,the alpha phase corundum oxide (α-Al₂O₃) is not suitable for use as adielectric and is accordingly associated with undesirably high levels ofleakage and deformation. However, alpha phase corundum oxide (α-Al₂O₃)is very stable and is difficult to convert back into the boehmite phaseof aluminum oxide. While adjustments to the laser cutting parametersdisclosed above can partially address the leakage and deformationassociated with the this conversion from the first phase of the anodemetal oxide to the second phase of the anode metal oxide, an oxideextraction phase discussed in more detail below can further reduce theleakage and deformation caused by this conversion.

The process of extracting the anode precursor 56 from the sheet ofmaterial 48 can leave the anode metal 14 exposed at the edges of theanode precursor 56. In some instances, a hydration layer is optionallyformed on the exposed anode metal 14. The hydration process builds anon-voltage supporting hydration layer that helps to both create ahigher quality anode metal oxide 12 and speed up its formation during asubsequent aging process. The hydration process lowers the aging time byusing a hydration oxide backbone to speed formation of the anode metaloxide 12 during aging. In some instances, the hydration process cleansup the edges of anode precursor 56 by “smoothing” any metal burrs on theedges. The detachment of the burrs and “smoothing” can be increased byuse of sonic or ultrasonic vibrational energy when forming the hydrationlayer.

A suitable method of creating the hydration layer includes, but is notlimited to, immersing at least a portion of the anode precursor 56 in abath that includes, consists of, or consists essentially of water. Inone example, the water is de-ionized. The bath may be held at atemperature between 60 and 100 degrees C., and preferably at about 95degrees C. The anode precursor 56 may remain immersed in the bath for aperiod of time greater than 2 minutes and/or less than 20 minutes toform the hydration layer. In some instances, the bath is sonicated ateither sonic or ultrasonic frequencies. The formation of the hydrationlayer will help to form a better quality oxide during a subsequent agingprocess.

A passivation layer can optionally be formed on the exposed anode metalthat is not covered by the anode metal oxide or the hydrate of the anodemetal. A suitable method for forming the passivation layer includes, butis not limited to, immersing at least a portion of the anode precursor56 in a second bath that includes, consists of, or consists essentiallyof ammonium dihydrogen phosphate. In some instances, the second bath ismaintained at a temperature greater than 52° C. and/or less than 90° C.,or 70° C. Additionally or alternately, the second bath can contain morethan 0.1 wt %, or 5.0 wt %, and/or less than 2.0 wt % ammoniumdihydrogen phosphate. The anode precursor 56 can be at least partiallyimmersed in the second bath for a time greater than one minutes and/orless than four minutes. After removing the anode precursor 56 from thesecond bath, the anode precursor 56 can be rinsed under de-ionized waterfor a time greater than one minute and/or less than 12 minutes.

The one or more anode precursors 56 constructed according to FIG. 2Athrough FIG. 2G are included in a capacitor precursor 61 according toFIG. 2I. For instance, one or more of the anode precursors 56 arecombined with one or more separators 24 and one or more cathodes 16 soas to form an electrode assembly 22 with the components arranged asdisclosed in the context of FIG. 1A through FIG. 1E. The electrodeassembly 22 is placed in a capacitor case 26 along with the electrolyte40. Any electrical connections needed for operation of the capacitorprecursor 61 are made and the capacitor case 26 is sealed.

The capacitor precursor 61 can optionally be put through an aging phase.The aging phase can be configured to form an anode metal oxide 12 on theedges of the one or more anode precursors 56 in the capacitor and/or onany other exposed anode metal 14. The aging process can use water in theelectrolyte 40 to form the oxide. The phase of the anode metal oxide 12formed during the aging phase is not necessarily the same as the firstphase of the anode metal oxide 12. For instance, when the anode metal 14is aluminum, the anode metal oxide 12 formed during the aging phase isnot the boehmite phase but is similar. Suitable methods for aging thecapacitor precursor 61 include, but are not limited to, holding thecapacitor at an elevated temperature while charged. For instance, insome instances, aging includes holding the capacitor at a temperaturegreater than 50° C. or 70° C. and/or less than 100° C. or 200° C. for atime greater than 2 hours or 20 hours, and/or less than 50 hours or onehundred hours while charged to a voltage greater than 50 V or 200 Vand/or less than 600 V or 800 V. In one example, aging includes holdingthe capacitor at about 85° C. for 24 to 36 hours while charged to about400 V.

The capacitor precursor 61 can optionally be put through a testingphase. The testing phase can be configured to test the capacitorprecursor 61 for charge and discharge functionality.

An oxide phase extraction is performed on the capacitor precursor 61.The oxide phase extraction can include an oxide removal stage thatremoves all or a portion of the second phase of the anode metal oxidefrom the anode precursor 56 and/or from the portion of the sheet ofmaterial 48 that serves as the anode precursor 56. In some instances,the oxide phase extraction moves all or a portion of the second phase ofthe anode metal oxide 12 from the anode precursor 56 into theelectrolyte 40. The oxide phase extraction can be performed such thatthe first phase of the anode metal oxide 12 remains intact or remainssubstantially intact. The oxide phase extraction can also include anoxide restoration stage that forms the anode metal oxide 12 on exposedanode metal 14 and/or on areas where the anode metal oxide 12 is thin.As a result, the oxide restoration stage can restore the first phase ofthe anode metal oxide that is removed or damaged during the oxideremoval stage. The phase of the anode metal oxide 12 formed during theoxide restoration stage can be the first phase of the anode metal oxide12. Suitable methods for the oxide restoration stage can be the same orsimilar to the methods used in the aging phase.

An example oxide phase extraction includes one or more cycles. Eachcycle can include the oxide removal stage followed by the oxiderestoration phase. When the oxide phase extraction includes multiplecycles, the cycles can be repeated in series. An example oxide phaseextraction includes a high temperature stage that acts as an oxideremoval stage followed by a low temperature stage and a charging stage.The low temperature stage can be performed between the high temperaturestage and the charging stage. The high temperature stage can beconfigured to move all or a portion of the second phase of the anodemetal oxide 12 from the anode precursor 56 and into the electrolyte 40.The low temperature stage can be configured to form the first phase ofthe anode metal oxide 12 on any anode metal 14 that becomes exposedduring the high temperature stage. The charging stage causes a currentsurge through the anode precursor 56 that reforms the anode metal oxide12. For instance, the charging stage can form the first phase of theanode metal oxide 12 on the anode precursor 56 from oxygen in theelectrolyte 40. Accordingly, the low temperature stage and the chargingstage together can serve as an oxide restoration stage.

An example of a single cycle of the oxide phase extraction includes ahigh temperature stage where the capacitor precursor 61 is exposed to atemperature T₁ for a time period P₁; a low temperature stage where thecapacitor precursor 61 is exposed to a temperature T₂ for a time periodP₂; and a charging stage where the capacitor precursor 61 is charged toV₁ and discharged. The cycle of the oxide phase extraction can beperformed 1-10 times. In some embodiments, the cycle of the oxide phaseextraction can be performed more than 10 times.

Examples of suitable T₁ include, but are not limited to, T₁ greater than45° C., or 50° C. and/or less than 90° C. or 100° C. In some instances,prolonged exposure of the capacitor to temperatures above 90° C. candamage one or more components of the capacitor. Examples of suitable P₁include, but are not limited to, P₁ greater than 0.5 hours and/or lessthan 2 days. The variables T₁ and P₁ can be a function of materialsand/or configuration. Additionally, the value of P₁ can be a function ofT₁. Exposure of a capacitor precursor 61 to increased temperatures forprolonged periods of time can damage the capacitor precursor 61components. As a result, as T₁ increases, it is generally desirable toreduce the value of P₁. For example, when T₁ is above 85° C., P₁ can beless than 2 hours but when T₁ is below 50° C., P₁ can be more than 1day.

Examples of suitable T₂ include, but are not limited to, T₂ greater than35° C., or 45° C. and/or less than 50° C. or 70° C. Examples of suitableP₂ include, but are not limited to, P₂ greater than 10 minutes and/orless than 100 minutes or one day. In some instances, T₁ is higher thanT₂ but P₁ is longer than P₂. Examples of suitable V₁ include, but arenot limited to, V₁ greater than 200 V or 400V and/or less than 500V or600V. Examples of suitable N include, but are not limited to, N greaterthan 0, 1, or 8 and/or less than 15, 25, or 35.

An example of the oxide phase extraction includes any one, any two, anythree, any four, any five, or any six features selected from the groupconsisting of T₁ greater than 45° C., or 50° C. and/or less than 90° C.or 100° C., P₁ greater than 0.5 hours and/or less than 2 days, T₂greater than 35° C. or 45° C. and/or less than 50° C. or 70° C., P₂greater than 10 minutes and/or less than 100 minutes or one day, V₁greater than 200 V or 400V and/or less than 500V or 600V. In someinstances, this oxide phase extraction is performed for a number ofcycles, N, greater than 0, 1, or 8 and/or less than 15, 25, or 35.

When the anode metal 14 is aluminum and the first phase of the anodemetal oxide 12 is the boehmite phase of aluminum oxide, an example of acycle the oxide phase extraction includes a high temperature stage wherethe capacitor precursor 61 is placed in a 90° C. (+/−5° C.) oven for 1hour (+/−5 min); a low temperature stage where the capacitor precursor61 is placed in a 37° C. (+/−5° C.) oven for 30 minutes (+/−5 min); acharging stage where the capacitor precursor 61 is charged to 422.5Volts and discharged. To execute the oxide phase extraction, this cycleof the oxide phase extraction can be performed once or sequentiallyrepeated for 1 or more cycles to 35 or fewer cycles. The total number ofcycles performed can be a function of the capacitor response to thepreceding cycles. For instance, performance of additional cycles can beoptional or skipped once the time needed to charge the capacitor after acycle is less than a threshold. In one example, the threshold is 5% ofthe time needed to charge the capacitor before the cycle.

The exact number of cycles needed can be a function of the properties ofthe sheet of material 48 and the thermal effect of laser cutting on theedge. As a result, the number of cycles that are performed can bevariable. For example, the time needed to charge the capacitor precursor61 can be measured after each cycle. The measured charge time can becompared to a charge time threshold. If the charge time for cycle jexceeds the threshold, then an additional cycle can be performed. Whenthe charge time for cycle j falls below the threshold, additional cyclesare not performed. For instance, the threshold can be a percentage ofthe time needed to charge the capacitor after the immediately precedingcycle. In one example, the threshold is 5% of the time needed to chargethe capacitor before the cycle.

Completion of the oxide extraction phase provides the anode andcapacitor of FIG. 1A through FIG. 1G. Accordingly, the capacitor isready for use in the desired application and/or for resale.

Example 1

A first anode precursor, second anode precursor, third anode precursor,and a fourth anode precursor were fabricated as described above. Forinstance, the anode precursors were formed using an aluminum foil as theanode metal. The surface area enhancement phase and oxide formationphase were performed on the aluminum foil so as to provide the sheet ofmaterial. The conditions of the surface area enhancement phase and theoxide formation phase were the same for the first anode precursor andthe second anode precursor.

The first anode precursor was extracted from the sheet of material usinga laser having a pulse duration of 820 femtoseconds, a pulse frequencyof 400,000 pulses per second, and a power density on the face of thesheet of material of 8×10¹¹ W/cm. The laser beam was traced on the faceof the sheet of material along a pathway having the shape desired forthe perimeter of an anode precursor. The beam speed at the face of thesheet of material was 110 mm/s, a spot overlap was 99.50%, and sixpasses were required in order to completely separate the anode precursorfrom the sheet of material.

The second anode precursor was extracted from the sheet of materialusing a laser having a pulse duration of 820 femtoseconds, a pulsefrequency of 400,000 pulses per second, and a power density on the faceof the sheet of material of 1×10¹² W/cm. The laser beam was traced onthe face of the sheet of material along a pathway having the shapedesired for the perimeter of an anode precursor. The beam speed at theface of the sheet of material was 310 mm/s, a spot overlap was 98.60%,and twelve passes were required in order to completely separate theanode precursor from the sheet of material.

The third anode precursor was extracted from the sheet of material usinga laser having a pulse duration of 820 femtoseconds, a pulse frequencyof 400,000 pulses per second, and a power density on the face of thesheet of material of 1×10¹² W/cm. The laser beam was traced on the faceof the sheet of material along a pathway having the shape desired forthe perimeter of an anode precursor. The beam speed at the face of thesheet of material was 440 mm/s, a spot overlap was 98.0%, and 20 passeswere required in order to completely separate the anode precursor fromthe sheet of material.

The fourth anode precursor was extracted from the sheet of materialusing a laser having a pulse duration of 820 femtoseconds, a pulsefrequency of 400,000 pulses per second, and a power density on the faceof the sheet of material of 8×10¹¹ W/cm. The laser beam was traced onthe face of the sheet of material along a pathway having the shapedesired for the perimeter of an anode precursor. The beam speed at theface of the sheet of material was 720 mm/s, a spot overlap was 96.7%,and sixty passes were required in order to completely separate the anodeprecursor from the sheet of material.

FIG. 3A is a Scanning Electron Microscope image of an edge of the firstanode precursor. This image shows the presence of re-solidified materialon the edge of the first anode precursor. FIG. 3B is a Scanning ElectronMicroscope image of an edge of the second anode precursor. This imageshows the presence of re-deposited material on the edge of the secondanode precursor. FIG. 3C is a Scanning Electron Microscope image of anedge of the third anode precursor. This image shows the absence of bothre-solidified material and re-deposited material on the edge of thesecond anode precursor. FIG. 3D is a Scanning Electron Microscope imageof an edge of the fourth anode precursor. This image shows the absenceof both re-solidified material and re-deposited material on the edge ofthe second anode precursor.

Example 2

The method of anode fabrication described in the context of FIG. 2Athrough FIG. 2I was followed to fabricate a first capacitor, a secondcapacitor, and a third capacitor. The first capacitor, the secondcapacitor, and the third capacitor each included anodes formed using analuminum foil as the anode metal. The surface area enhancement phase andoxide formation phase were performed on the aluminum foil so as toprovide the sheet of material. The variables for the surface areaenhancement phase and the oxide formation phase were the same oressentially for each of the capacitors.

The first capacitor was prepared using anodes constructed from anodeprecursors constructed according to the first anode precursors ofExample 1. The second capacitor was prepared using anodes constructedfrom anode precursors constructed according to the second anodeprecursors of Example 1. The third capacitor was prepared using anodesconstructed from anode precursors constructed according to the thirdanode precursors of Example 1.

Each capacitor was assembled with 45 anodes (˜115 microns thick each)stacked with 10 aluminum foil cathodes (˜12 microns thick each) and anethylene glycol based electrolyte that included boric acid. Separatorsof 1.06 Density Kraft Paper at ˜20 microns thickness were positionedbetween adjacent anodes and cathodes. An aging phase and a testing phasewere performed on each of the capacitors. The conditions for the agingphase and testing phase were the same for each of the capacitors.

The capacitors were each run through a series of downs and tested forthe level of deformation at each down. A down for a capacitor simulatesthe aging that a capacitor experiences when used in an ImplantableCardioverter Defibrillator (ICD) that is implanted in a patient for a 3month period of time. A down can be simulated by exposing the capacitorto heat. For each of the downs, the capacitors were maintained at about90° C. for about 16 hours. After every down or every other down, thecapacitors were tested for deformation. Deformation is a measure of thechange in the amount of time required to charge the capacitor relativeto a baseline time. For instance, the deformation for down i can bemeasured as ((down i charge time)/(baseline charge time)−1)×100% wherethe baseline charge time is the time needed to charge the capacitor attime i=1. The charging source used for each deformation measurement wasthe same.

The results of the above measurements are presented in FIG. 4A. Theresults for the first capacitor are labeled “first capacitor” in FIG.4A. The results for the second capacitor are labeled “second capacitor”in FIG. 4A. The results for the third capacitor are labeled “thirdcapacitor” in FIG. 4A. The laser cutting parameters used to generateFIG. 4A did not bring the deformation below 100% without the use of anoxide phase extraction.

Example 3

The method of anode fabrication described in the context of FIG. 2Athrough FIG. 2I was followed to fabricate a first capacitor, a secondcapacitor, and a third capacitor. The first capacitor, the secondcapacitor, and the third capacitor each included anodes formed using analuminum foil as the anode metal. The surface area enhancement phase andoxide formation phase were performed on the aluminum foil so as toprovide the sheet of material. The variables for the surface areaenhancement phase and the oxide formation phase were the same oressentially for each of the capacitors.

The anodes precursors for the first capacitor, second capacitor, andthird capacitor were laser cut from the sheet of material using the samelaser.

The anode precursors for the first capacitor were extracted from thesheet of material using a laser having a pulse duration of 820femtoseconds, a pulse rate of 400,000 pulses per second, and a powerdensity on the face of the sheet of material of 8×10¹¹ W/cm. The laserbeam was traced on the face of the sheet of material along a pathwayhaving the shape desired for the perimeter of an anode precursor. Thebeam speed at the face of the sheet of material was 110 mm/sec, the spotoverlap was 99.50%, and 6 passes were required in order to completelyseparate the anode precursor from the sheet of material.

The anode precursors for the second capacitor were extracted from thesheet of material using a laser having a pulse duration of 820femtoseconds, a pulse rate of 400,000 pulses per second, and a powerdensity on the face of the sheet of material of 1×10¹² W/cm. The laserbeam was traced on the face of the sheet of material along a pathwayhaving the shape desired for the perimeter of an anode precursor. Thebeam speed at the face of the sheet of material was 310 mm/sec, the spotoverlap was 98.6%, and 12 passes were required in order to completelyseparate the anode precursor from the sheet of material.

The anode precursors for the third capacitor were extracted from thesheet of material using a laser having a pulse duration of 820femtoseconds, a pulse rate of 400,000 pulses per second, and a powerdensity on the face of the sheet of material of 1×10¹² W/cm. The laserbeam was traced on the face of the sheet of material along a pathwayhaving the shape desired for the perimeter of an anode precursor. Thebeam speed at the face of the sheet of material was 440 mm/sec, the spotoverlap was 98.0%, and 20 passes were required in order to completelyseparate the anode precursor from the sheet of material.

Each capacitor was assembled with 45 anodes (˜115 microns thick each)stacked with 10 aluminum foil cathodes (˜12 microns thick each) and anethylene glycol based electrolyte that included boric acid. Separatorsof 1.06 Density Kraft Paper at ˜20 microns thickness were positionedbetween adjacent anodes and cathodes. An aging phase and a testing phasewere performed on each of the capacitors. The conditions for the agingphase and testing phase were the same for each of the capacitors.

The capacitors were each run through a series of downs and tested forthe level of deformation at each down. For each of the downs, thecapacitors were maintained at about 90° C. for about 16 hours. Afterevery down or every other down, the capacitors were tested fordeformation. Deformation is a measure of the change in the amount oftime required charge the capacitor relative to a baseline time. Forinstance, the deformation for down i can be measured as ((down i chargetime)/(baseline charge time)−1)×100% where the baseline charge time isthe time needed to charge the capacitor at time i=1. The charging sourceused for each deformation measurement was the same.

The results of the above measurements are presented in FIG. 4B. Theresults for the first capacitor are labeled “first capacitor” in FIG.4B. The results for the second capacitor are labeled “first capacitor”in FIG. 4B. The results for the third capacitor are labeled “firstcapacitor” in FIG. 4B. FIG. 4B shows that adjusting laser cuttingparameters can bring deformation below 20% without the use of an oxidephase extraction. In contrast, using stamping to cut anodes out of asimilar sheet of material provides deformation levels above 25% atapproximately down 10 downs. This result shows that selection of lasercutting parameters can bring deformation levels at or below the levelassociated with stamping of the anodes.

Example 4

The method of anode fabrication described in the context of FIG. 2Athrough FIG. 2I was followed to fabricate a first capacitor and a secondcapacitor. For instance, the first capacitor and the second capacitoreach included anodes formed using an aluminum foil as the sheet ofmaterial in performing the surface area enhancement phase, oxideformation phase, and laser cutting so as to remove the anodes from theresulting sheets of material. The first capacitor and the secondcapacitor were each assembled with 45 anodes (˜115 microns thick each)stacked with 10 aluminum foil cathodes (˜12 microns thick each) and anethylene glycol based electrolyte that included boric acid. Separatorsof 1.06 Density Kraft Paper at ˜20 microns thickness were positionedbetween adjacent anodes and cathodes.

An aging phase and a testing phase were performed on the first capacitorand the second capacitor. The conditions for the surface areaenhancement phase, oxide formation phase, laser cutting, aging phase andtesting phase were the same for the first capacitor and the secondcapacitor. The laser cutting was performed by a Trumpf TruMicro5050 fsedition laser having a pulse duration of 820 femtoseconds, a pulse rateof 400,000 pulses per second, and a power density on the face of thesheet of material of 8×10¹¹ W/cm. The laser beam was traced on the faceof the sheet of material along a pathway having the shape desired forthe perimeter of an anode precursor. The beam speed at the face of thesheet of material was 720 mm/sec, the spot overlap was 96.7%, and 60passes were required in order to completely separate the anode precursorfrom the sheet of material. An oxide phase extraction was performed onthe second capacitor but not on the first capacitor. The oxide phaseextraction had a cycle that included a high temperature stage where thesecond capacitor was placed in a ˜90° C. oven for about 1 hour; a lowtemperature stage where the second capacitor was placed in a ˜37° C.oven for about 30 minutes; and a charging stage where the secondcapacitor was charged to ˜422.5 Volts and discharged. The cycles of theoxide phase extraction were performed sequentially for 10 cycles.

The first capacitor and the second capacitor were disassembled and theanodes examined. FIG. 5A is a Scanning Electron Microscope image of anedge of an anode from the first capacitor. The portion of the imagewithin the line labeled A is believed to be alpha phase corundum oxide(α-Al₂O₃) positioned on boehmite aluminum oxide. FIG. 5B is a ScanningElectron Microscope (SEM) image of an edge of an anode from the secondcapacitor. The alpha phase corundum oxide (α-Al₂O₃) that is evident inFIG. 5A is not evident in FIG. 5B. The alpha phase corundum oxide isremoved during the high temperature stage of the oxide phase extraction.In particular, the high temperature stage of the oxide phase extractionactivates a reaction between a component of the electrolyte and thealpha phase corundum oxide (α-Al₂O₃). For instance, without being boundto theory, it is believed that the high temperature stage causes ahydration reaction between the alpha phase corundum oxide (α-Al₂O₃) andwater in the electrolyte and that the reaction product moves off thesurface of the anode and into the electrolyte.

Example 5

The method of anode fabrication described in the context of FIG. 2Athrough FIG. 2I was followed to fabricate a first capacitor, a secondcapacitor, a third capacitor and a fourth capacitor. The firstcapacitor, the second capacitor, the third capacitor, and the fourthcapacitor each included anodes formed using an aluminum foil as thesheet of material in performing the surface area enhancement phase,oxide formation phase. The variables for the surface area enhancementphase and the oxide formation phase were the same or essentially thesame for each of the capacitors.

The anodes in the first capacitor were extracted from the sheet ofmaterial 48 using die cutting rather than laser cutting. The anodes inthe second capacitor, third capacitor and fourth capacitor were lasercut from the sheet of material using the same 820 femtosecond laser. Thecutting conditions for the anodes in the second capacitor were differentfrom the cutting conditions for the anodes in the third capacitor. Forthe second capacitor, the laser was set at a pulse rate of 400,000pulses per second, and a power density on the face of the sheet ofmaterial of 1×10¹² W/cm. The laser beam was traced on the face of thesheet of material along a pathway having the shape desired for theperimeter of an anode precursor. The beam speed at the face of the sheetof material was 440 mm/sec, the spot overlap was 98.6% and 20 passes.For the third capacitor, the laser was set at a pulse rate of 400,000pulses per second, and a power density on the face of the sheet ofmaterial of 8×10¹¹ W/cm. The laser beam was traced on the face of thesheet of material along a pathway having the shape desired for theperimeter of an anode precursor. The beam speed at the face of the sheetof material was 720 mm/sec, the spot overlap was 96.7%, and 60 passes.The anodes of the fourth capacitor were cut under the same laserconditions as the anodes of the third capacitor.

Each capacitor was assembled with 45 anodes (˜115 microns thick each)stacked with 10 aluminum foil cathodes (˜12 microns thick each) and anethylene glycol based electrolyte that included boric acid. Separatorsof 1.06 Density Kraft Paper at ˜20 microns thickness were positionedbetween adjacent anodes and cathodes. The conditions for the aging phaseand testing phase were the same for each of the capacitors. An oxidephase extraction was performed on the fourth capacitor but not on thefirst capacitor, the second capacitor, or the third capacitor. The oxidephase extraction had a cycle that included a high temperature stagewhere the second capacitor was placed in a ˜90° C. oven for about 1hour; a low temperature stage where the second capacitor was placed in a37° C. oven for about 30 minutes; and a charging stage where the secondcapacitor was charged to ˜422.5 Volts and discharged. The oxide phaseextraction was performed for 10 sequential cycles.

The capacitors were each run through a series of downs and tested forthe level of deformation at each down. A down for a capacitor simulatesthe aging that a capacitor experiences when used in an ImplantableCardioverter Defibrillator (ICD) that is implanted in a patient for a 3month period of time. A down can be simulated by exposing the capacitorto heat. For each of the downs, the capacitors were maintained at about90° C. for about 16 hours. After every other down, the capacitors weretested for deformation. Deformation is a measure of the change in theamount of time required to charge the capacitor relative to a baselinetime. For instance, the deformation for down i can be measured as ((downi charge time)/(baseline charge time)−1)×100% where the baseline chargetime is the time needed to charge the capacitor at time i=1. Thecharging source used for each deformation measurement was the same.

The results of the above measurements are presented in FIG. 6. Theresults for the first capacitor are labeled “die cut” in FIG. 6. Theresults for the second capacitor are labeled “no phase extraction 1” inFIG. 6. The results for the third capacitor are labeled “no phaseextraction 2” in FIG. 6. The results for the fourth capacitor arelabeled “phase extraction” in FIG. 6.

The results in FIG. 6 show a positive slope for the first capacitor.This positive slope is believed to be caused by incorporation of ironfrom the die in the unformed edges of the anodes during aging. Thesecond capacitor and the third capacitor provide curves that start atelevated higher levels of deformation and then drop down to a flatterand more consistent slope. This result is believed to occur because theuse of laser cutting to cut the anodes reduces the presence of the ironat the edges of the anodes. The fourth capacitor starts at significantlylower levels of deformation than either the second capacitor or thethird capacitor and then stays at these reduced levels for subsequentdowns. The ability of the fourth capacitor to start and stay at reduceddeformation levels means that less energy is required to charge thecapacitor over the life of the capacitor.

Example 6

The results achieved in Example 2 were unexpected. History has shownthat putting energy into the capacitor before the first down can cause adrop in the level deformation shown at the first down. However, thisdrop in deformation has proven to be temporary and the deformation risestoward it original value in subsequent downs. As an example, FIG. 7 addsa curve labeled “expected result” to FIG. 6. Rather than performing anoxide phase extraction, the capacitor was put through 52 cycles wherethe capacitor was repeatedly charged and discharged. As expected, thiscurve shows that the level of deformation increases after the initialdrop in deformation. In contrast, the curve labeled “phase extraction”does not show a temporary drop in the level of deformation. Theunexpected retention of the reduced deformation levels is believed to bethe result of the alpha phase corundum oxide (α-Al₂O₃) moving into theelectrolyte.

Example 7

A sheet of material was generated as disclosed in the context of FIG. 2Athrough FIG. 2E. The sheet of material was warped as shown in FIG. 8A. Athermal treatment was performed on the sheet of material. The thermaltreatment included a low pressure compression followed by a highpressure compression. The low pressure compression and the high pressurecompression were performed using plates as compression members. Thecompression members were located in an oven in order to keep thecompression surfaces as the desired compression temperature. The lowpressure compression was performed for a compression time of 5 seconds,a compression temperature of 500° C., at a compression pressure of 0.1psi. The high pressure compression was performed for a compression timeof 10 seconds, a compression temperature of 500° C., at a compressionpressure of 1 psi. The results of the thermal treatment are shown inFIG. 8B.

Example 8

First capacitors included first anodes that were generated withoutthermal compression. The first anodes were cut from a sheet of materialgenerated as disclosed in the context of FIG. 2A through FIG. 2E. Aseries of four anode oxide formation operations were performed on asheet of material. A thermal treatment was performed after each of theanode oxide formation operations. The thermal treatments were eachperformed by placing the sheet of material in an oven at 500° C. forfour minutes.

Second capacitors included second anodes that were generated withthermal compression. The second anodes were cut from a sheet of materialgenerated under conditions similar to the sheet of material used in thefirst capacitors. A series of four anode oxide formation operations wereperformed on a sheet of material under conditions similar to theconditions of the anode oxide formation operations used to generate theanodes. A thermal treatment was performed after each of the anode oxideformation operations. The thermal treatment performed after the secondanode oxide formation operation included thermal compression. Incontrast, the thermal treatment performed after the first, third andfourth anode oxide formation operations did not included thermalcompression. In particular, the thermal treatments performed after thefirst, third and fourth anode oxide formation operations were performedby placing the sheet of material in an oven at 500° C. for 4 minutes.The thermal treatment performed after the second anode oxide formationoperation included a single compression operation. The compressionoperation was performed using plates as compression members. Thecompression members were located in an oven in order to keep thecompression surfaces as the desired compression temperature. Thecompression operation was performed for a compression time of 1 minute,at a compression temperature of 400° C., at a compression pressure of0.1 psi.

The capacitors were each run through a series of downs and tested forthe level of deformation at each down as described above in Example 2.The results for the first capacitors are presented in FIG. 9A. Theresults for the first capacitors are presented in FIG. 9B. Despite usingonly one thermal compression at a low compression temperature, thesecond capacitors show improved deformation performance. The improvementin deformation can lead to increased longevity of a device such as anImplantable Cardioverter Defibrillator (ICD) device by improving thecapM time interval from 4-6 months to 9-12 months. Additionally, thesecond capacitors show reduced variability in deformation. The inventorsbelieve that the second capacitors would show even lower levels ofdeformation at higher compression temperatures, such as 500° C.

Additionally, the second capacitors showed a 5.5% higher foilcapacitance than the first capacitors. The leakage current for thesecond capacitors increased from 144.8 μA to 261.0 μA. However, leakageis not as important of a performance indicator in applications where apotential is only occasionally applied to the capacitors such as inICDs. Further, the inventors believe that leakage of the secondcapacitors can be reduced by using higher compression temperatures, suchas 500° C.

The above capacitors can be used in medical devices such as anImplantable Cardioverter Defibrillator (ICD). FIG. 10 is a schematicdiagram of a defibrillation system that includes an ImplantableCardioverter Defibrillator (ICD) that employs one or more capacitorsconstructed as disclosed above. The defibrillation system includes leadlines 62 connected to electrodes 64 in contact with the heart. Althoughthe defibrillation system is shown with two electrodes 64, thedefibrillation system may include three or more electrodes 64 and/orthree or more lead lines. The specific positions of the electrodes 64relative to the heart 66 is dependent upon the requirements of thepatient.

The defibrillation system also includes a processing unit 68. The leadlines 62 provide electrical communication between the processing unit 68and the electrodes 64. The processing unit 68 is also in electricalcommunication with one or more capacitors constructed as disclosedabove.

The processing unit 68 receives power from a battery 72. The processingunit 68 can place the battery 72 in electrical communication with theone or more capacitors 70. For instance, the processing unit 68 cancause the battery 72 to charge the one or more capacitors 70.Additionally, the processing unit 68 can place the one or morecapacitors 70 in electrical communication with the lead lines 62. Forinstance, the processing unit 68 can cause the one or more capacitors tobe discharged such that electrical energy stored in the one or morecapacitors is delivered to the heart through all or a portion of theelectrodes 64. The processing unit 68, the battery 72 and the one ormore capacitors 70 are positioned in a case 84.

During operation of the defibrillation system, the defibrillation systememploys output from the lead lines 62 to monitor the heart and diagnosewhen defibrillation shocks should be provided. When the processing unit68 identifies that defibrillation shocks are needed, the processing unit68 provides the heart with one or more defibrillation shocks. To providea defibrillation shock, the processing unit 68 employs energy from thebattery 72 to charge the one or more capacitors 70. Once the one or morecapacitors are charged, the processing unit 68 causes these capacitorsto be discharged such that energy stored in the capacitors is deliveredto the heart through all or a portion of the electrodes 64 in the formof defibrillation shocks. During the defibrillation shocks, thedefibrillator requires that one or more pulses be delivered from thebattery 72 to the one or more capacitors. Each pulse is generallyassociated with a defibrillation shock. The duration of each pulse isgenerally about 8 to 12 seconds with the pulses separated by a delaytime that is based on how fast the battery charges the capacitor anddetermining the appropriate point to provide the defibrillation shock.

Suitable processing units 68 can include, but are not limited to, analogelectrical circuits, digital electrical circuits, processors,microprocessors, digital signal processors (DSPs), computers,microcomputers, or combinations suitable for performing the monitoringand control functions. In some instances, the processing unit 68 hasaccess to a memory that includes instructions to be executed by theprocessing unit 68 during performance of the control and monitoringfunctions.

The sequence of events disclosed above for forming an anode can beperformed in a sequence other than the disclosed sequence. For instance,the oxide phase extraction can be performed on the anode before thecapacitor is assembled. As another example, the aging phase can beperformed after the testing phase.

Although the above methods of forming an anode have been disclosed inthe context of a capacitor, the above oxide phase extraction can also beapplied to the fabrication of anodes, cathodes, positive electrodes,and/or negative electrodes in batteries.

Other embodiments, combinations and modifications of this invention willoccur readily to those of ordinary skill in the art in view of theseteachings. Therefore, this invention is to be limited only by thefollowing claims, which include all such embodiments and modificationswhen viewed in conjunction with the above specification and accompanyingdrawings.

What is claimed is:
 1. A method for fabricating a capacitor, comprising:performing an oxide formation operation on a sheet of material, theoxide formation operation forming an anode metal oxide on an anodemetal; performing a thermal compression operation on the sheet ofmaterial after performing the oxide formation operation; and assemblingthe capacitor after performing the thermal compression operation, thecapacitor being generated such that an electrode included in thecapacitor includes at least a portion of the sheet of material.
 2. Themethod of claim 1, wherein forming the anode metal oxide includesconverting a portion of the anode metal to the anode metal oxide.
 3. Themethod of claim 1, wherein forming the anode metal oxide includes anodicoxidation of the anode metal.
 4. The method of claim 1, wherein thethermal compression operation removes water from the anode metal oxide.5. The method of claim 1, wherein the thermal compression operationincludes compressing the sheet of material while applying thermal energyto the sheet of material.
 6. The method of claim 5, wherein the sheet ofmaterial is compressed between multiple compression members.
 7. Themethod of claim 6, wherein the compression members each includes acompression surface that is in direct physical contact with the sheet ofmaterial while the sheet of material is compressed between compressionmembers.
 8. The method of claim 7, wherein the compression surfaces areplanar.
 9. The method of claim 7, wherein at least one of thecompression surfaces is at a compression temperature greater than 300°C. while the sheet of material is compressed between compressionmembers.
 10. The method of claim 9, wherein the compression temperatureis from 300° C. to 600° C.
 11. The method of claim 6, wherein a periodof time for which the sheet of material is compressed between multiplecompression members is greater than 5 seconds and less than 10 minutes.12. The method of claim 1, wherein the thermal compression operationinclude applying pressure of more than 1 ounce/square inch to the sheetof material.
 13. The method of claim 12, wherein a temperature of atleast a portion of the sheet of material is increased to more than 300°C. during the thermal compression operation.
 14. The method of claim 13,wherein the pressure of more than 1 ounce per in² for a period of timeless than 10 minutes.
 15. The method of claim 1, wherein the thermalcompression operation is one of several thermal compression operationsperformed on the sheet of material; the oxide formation operation is oneof several oxide formation operations performed on the sheet ofmaterial; and the thermal compressions are alternated with the oxideformation operations.
 16. The method of claim 1, wherein the thermalcompression operation includes multiple thermal compressions performedin series such that different thermal compressions apply differentlevels of pressure to the sheet of material.
 17. The method of claim 16,wherein the thermal compression operation includes a low pressurethermal compression followed by a high pressure thermal compression, alower level of pressure being applied to the sheet of material duringthe low pressure thermal compression than is applied during the highpressure thermal compression.
 18. The method of claim 17, wherein apressure between 0 psi and 0.1 psi is applied to the sheet of materialduring the low pressure thermal compression and a pressure between 0 psiand 1 psi is applied to the sheet of material during the high pressurethermal compression.
 19. The method of claim 18, wherein the pressureapplied to the sheet of material during the low pressure thermalcompression is applied for a compression time between 1 second and tenminutes and the pressure applied to the sheet of material during thehigh pressure thermal compression is applied for a compression timebetween 1 second and ten minutes.
 20. The method of claim 17, wherein apressure less than 0.5 psi is applied to the sheet of material duringthe low pressure thermal compression and a pressure between 0.5 psi and2 psi is applied to the sheet of material during the high pressurethermal compression.